Greenhouse gas emissions could cause global temperatures to rise by up to 11°C, according to first results from the world's largest climate modelling experiment.

The top end of the predictions, which range from 2 to 11°C, is double estimates produced so far.

The research, which was published in today's issue of the journal Nature, was made possible by harnessing computer power from around the world.

A total of 95,000 people from 150 countries took part in the project, the first results of which are published today.

These include 2441 users from Australia, who downloaded free software from www.climateprediction.net, and used their home computers' idle processing capacity to run a climate model.

"Our experiment shows that increased levels of greenhouse gases could have a much greater impact on climate than previously thought," says UK researcher David Stainforth, the project's chief scientist, from the University of Oxford.

Without significant cuts in greenhouse gas emissions, some scientists estimate the Earth's temperature and sea level will rise, leading to increased flooding and drastic climate changes.

The temperature range predicted is based on assumptions of carbon dioxide levels double those found before the Industrial Revolution. Some scientists estimate these levels will be reached by the middle of this century if greenhouse gas emissions are not reduced.

"This is really just the beginning of the process to try and understand the uncertainty and predictions of climate change," Stainforth adds.

Harnessing power

Computer users from Uruguay to Uzbekistan and Sierra Leone to Singapore have downloaded software from the climateprediction.net site, which allows them to run their own unique version of the UK's Met Office climate model.

While their computer is idle, the program runs a climate simulation over days or weeks and automatically reports the results to the University of Oxford and other collaborating institutions around the world.

Together, the volunteers have simulated more than 4 million model years, donated 8000 years of computer time and exceeded the processing power of the world's largest supercomputers.

"It is entirely possible that even current levels of greenhouse gases, if stable and maintained for a long period of time, could lead to dangerous climate change," Stainforth says.

The Kyoto protocol, the main UN scheme to reduce greenhouse gases, aims to cut emissions of carbon dioxide by 5.2% below 1990 levels by 2008-12.